Influence of exchange interaction on spin-dependent transport through a single quantum dot doped with a magnetic ion

摘要

A quantum theory of single-electron tunneling through a quantum dot (QD), doped with a Mn~(2+) ion and weakly coupled to ferromagnetic (FM) leads in the Coulomb blockade regime, is developed using the sequential tunneling approach and assuming that spin flips do not occur. It predicts a spin-injection-induced magnetization and a spin-dependent current. The spin polarization of the current and the tunneling magnetoresistance (TMR) can be well controlled by a bias voltage and strongly enhanced by the electron-Mn exchange interaction and the spin selectivity of the leads. An appropriate choice of these parameters yields a highly polarized current even when the FM source is not 100% polarized. Analytical expressions for the magnetization, spin-dependent current, spin polarization, and the TMR are derived for zero magnetic field. When the QD is subjected to a strong magnetic field, the numerical calculations predict an oscillatory behavior of the TMR as a function of the bias voltage.